The Side Texture node assign black or white values based on the normal direction of a polygon object. This is useful for assigning different textures or materials to different sides of a polygon object. Figure 1 shows how a Side texture is used to control the amount of a Mix texture. Yellow and red RGB Spectrum textures are connected to the Mix Texture.
Figure 1 : A Side texture is used to control the amount of a Mix texture that blends yellow and red RGB Spectrum texture.
Figure 2 shows a render of the twisted geometry that is assigned a material that uses the Side texture node. This technique is useful for creating a leaf or butterfly wing with different colors or materials applied to each side.
Figure 2 : A twisted surface showing a red texture mapped to one side of the polygon and a green texture mapped to the other.